> A 2x4 LEGO brick manufactured in 1958 will snap perfectly onto a brick molded this morning in Denmark, China, Hungary, Mexico, or the Czech Republic.

In the late 90ies, I regularly played with my uncle's old LEGOs from the late 60ies and early 70ies. They were stored in an unheated attic for 25 years. I remember that some of the old bricks didn't "snap" at all anymore to my newer bricks. They were either extremely difficult to stack onto a new brick, or didn't have any friction left.

There were some bricks from the very early days that were not made from ABS, nor did they have the current box and pin style. Those are often loose (or broken).

In my experience the bricks that didn’t snap well would have too many teeth marks